The present invention relates to a spinal electrode catheter for stimulating areas of the vertebral column and the spinal bone marrow subcutaneously. It is being found currently in medical and surgical practice that optimum results are obtainable in the treatment of pathological conditions attributable to trauma of the vertebral column, affecting the spinal bone marrow in some instances, by inserting electrodes to stimulate the areas where functions (especially motor functions) have been impaired by such trauma.
Given however that this is a therapy of relatively recent origin, the prior art embraces no indwelling catheters designed specifically for implantation of the electrodes utilized to stimulate these areas (referred to in medicine as epidural); instead, the general practice is to adapt conventional cardiac pacemaker catheters for epidural implantation. Clearly enough, such adaptations are not entirely satisfactory, ensuring neither a swift and secure subcutaneous implant (which may also need to be permanent) nor even a wholly efficient treatment, at least when compared with the potential of the devices employed as cardiac pacemakers: in effect, the terminals or sensing elements of conventional cardiac pacemaker electrodes are disposed at fixed distances from each other and from the external stimulator; moreover, there are obvious differences in proportions, given the particular structure of the cardiac muscle (altogether different from the vertebral regions), and in the basic architecture adopted for the purposes of insertion, given that the anchorage and positioning requirements are not the same for a cardiac site as for vertebral sites, and will also vary in the latter instance according to the particular area traumatized.
This last-mentioned factor is of great importance for the patient, who has to undergo surgery of a delicate nature (e.g. laminectomy, or the removal of a lateral portion from the neural arch of one or more vertebrae) so that a vertebral anchorage can be effected; such operations generally do not tend to be secure and effective, either from the medical standpoint or that of the clarity of the signal at the poles of the electrodes afforded by the adapted catheter, and therefore can result in additional and not inconsiderable discomfort for the patient. In a dedicated solution aimed at solving problems of this nature, U.S. Pat. No. 4,379,462 discloses an electrode catheter comprising a tubular sheath designed to accommodate a plurality of electrically conductive wires establishing a corresponding plurality of electrodes; one end of each wire passes through the wall of the sheath to connect with a ring secured to the exterior of the sheath itself and providing the pole of the relative electrode, the remaining end being attached to the stimulator. The rings are spaced apart at an identical and selected distance one from another in such a way as to give an evenly distributed subcutaneous stimulation. The tubular sheath is also provided internally with a suitably rigid but flexible metal core designed to favor a subcutaneous insertion and to maintain the desired configuration of the catheter once in place.
Even this solution betrays drawbacks, however: the subcutaneous insertion cannot be effected without the aid of a guide element, preferably a stilet, which ensures that the catheter is correctly placed but must be removed following implantation, so that the duration of the operation is extended; neither does the metal core fully guarantee the performance of the tubular sheath, whether in respect of the rigidity required for insertion or of the degree of flexibility needed to adapt the electrode catheter to the cavity it will ultimately occupy. A further drawback stems from the fact that the sheath does not afford a faultless internal seal, especially at the breakout of the electrode wires, where the type of closure adopted tends not to give the mechanical and physiological guarantees appropriate to the purpose in question.
Accordingly, the object of the present invention is to overcome the drawbacks mentioned above through the provision of a spinal electrode catheter for use in subcutaneous stimulation of the vertebral column and spinal bone marrow, which can be swiftly and securely implanted in the patient and connected in such a way as to maintain a clean, uninterrupted electrical signal, and features a general structure tailored mechanically and biotechnologically to suit the specific field of therapy applied to the vertebral column.